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FCC-ee optics tuning WG

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354/1-016

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FCC-ee optics tuning WG meeting
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65516078996
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Rogelio Tomas Garcia
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News, Jacqueline, Rogelio

Preferred new option is to have combined HV correctors and BPM attached to quadrupole.

Tomorrow's ATDC is devoted to dynamic effects with a status of the tuning WG. Maybe it would be the time to ask about the status of the 2 dipole option.

 

Dynamic effects both on Collider and Booster, Sofia

Tolerance of 40-60nm rms GM motion (fully uncorrelated) to allow 20-50% emittance growth without beam-beam and without feedback first. This is considered to cause too large luminosity loss.

Feedback can correct up to 1.6 Hz or, pushed, 3 Hz as this is a global feedbak. Frank suggested to use local feedback so that they could be faster e.g. in the IR.  

Simulations with feedback show a great improvement in emittance but still ~20% emittance growth. Girder high frequency response to included, which would deteriorate the picture. 

Power converter: PC clases are identified allowing for 20-40% emittance growth. This seems too optimistic, tighter tolerances would be needed.

The Plans are also presented. 

IP feedback should eventually be included. Jack described briefly current status of the feedback. Challenges concerning CPU+GPU time needs are discussed. Solenoid will need to be added too. Ideal IP feedback might be the first approximation.

 

BBA tests at LHC, Christian

First measurement of LHC arc BPM-quad misalignments.  Up to 1mm misalignments observed with some large error bars in the order of some 100s of um. This is partly due to a parabolic response in some BPMs. This parabolic response changes with tune matching that affects response matrix. Degeneracy of the response matrix (specially at 180 degrees) could be a source of problems.

Measurements were also taken by modulation all arcs while cancelling tunes. Deviations between different measurements is about 100 um. Artificial bumps of ~0.5mm were introduced and could be easily identified.

Independent quadrupoles are also used: Error bars are clearly lower at the level of 20um, reproducibility a bit worse, closer to 100 um.

 

Dy measurments, Tirsi

How far can we go in dp/p via radial steering? Emittance clearly evolves with partition numbers versus dp/p, and crossing of resonances.Losses are mostly due to momentum collimation and transverse aperture of the doublet. Safe range for momentum modulation is +-0.5%.

Dispersion is measured by fitting a 3rd order polynominal. Simulated measurements give huge systematic contributions in the horizontal plane.  With ideal BPMs uncertainty in IP Dx and Dy are 1.7um and 0.3um, respectively (meeting specs). Adding BPM errors the situation is very different. To stay with 1um Dy error BPM uncertainty needs to be 0.1 um in the FD!

BPM roll plays a smaller effect.

 

 

 

 

 

 

 

 

 

 

 

 

 

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